1. Field of the Invention
The present invention relates, in general, to electrical arc welding, electric arc welding electrodes, and condition of an arc welding electrode prior to using the electrode to weld two pieces of metal together.
2. Description of the Prior Art
It is well known in the arc welding art that prior to welding steel, for example, the electrodes used must be conditioned properly to avoid adverse defects in the welds. Common defects in welds include undercutting, improper tie ends, porosity, lack of fusion, and either over or under fillet size. One of the ways utilized to provide low hydrogen electrodes for adverse welding conditions requiring low hydrogen deposits is to double coat using a titania coating to assist in protecting the underlying low hydrogen coating with a view to reducing or eliminating porosity problems.
Specifically, hydrogen can adversely affect a weld and some steels under certain conditions. One source of this hydrogen is moisture in the electrode covering. For this reason proper storage, treatment and handling of electrodes is absolutely necessary to prevent a defective weld. This is especially important in the construction and erection of multiple story buildings which rely for their support and inner structure on welded steel beams. A defective weld can result in the collapse of a portion of a building or during subsequent inspection rejection of the weld. This requires rebuilding a portion of the metal inner structure of a skyscraper or other building sometimes at cost overruns of many millions of dollars.
Electrodes are manufactured to be within acceptable moisture limits consistent with the type of covering and strength of the weld metal to be used with the electrode. They are then packaged in a container which has been designed to provide the degree of moisture protection considered necessary by the industry for the type of covering involved. Electrodes can be maintained for many months under proper storage at normal room temperatures with relative humidity at 50% or less or in holding ovens. A main problem with these holding ovens is that on a particular construction site for example a multiple story skyscraper building, the holding ovens are usually not readily accessible to various welding sites as the structure is being erected. The welder usually removes from the holding ovens one or more electrodes needed for a welding job and carries them to a particular subsite.
In the past leather pouches have been used in combination with heavy leather gloves worn by the welder to remove the electrode from the holding oven for insertion into a pouch carried on a belt by the welder. However, in extremely cold climates such as the northeastern United States, Europe, Greenland and Canada in winter these electrodes rapidly lose heat and decrease to an unacceptable temperature prior to being engaged to make a weld. Moreover, after these electrodes are removed from the holding oven and placed in the pouch and lose temperature on some occasions their coverings absorb excessive atmospheric moisture. When this happens and the electrode is used a defective weld with hydrogen bubbles therein is created which adversely affects the strength and integrity of any subsequent weld. In most instances when these welds are inspected they are marked and checked for reworking, removal, and rewelding.
In the prior art if a welder detected that an electrode picked up excessive moisture use of the electrode was postponed until it is restored to a usable condition by replacement in the holding oven or in a drying oven. For example, a low hydrogen iron powder welding electrode of the E7048 American Welding Society (AWS) classification requires drying for 2 hours at a temperature of 245 degrees C plus or minus 15 degrees C. The recommendation or standard for storing the electrode in the holding oven is 28 degrees C to about 130 degrees C above ambient temperature.
The low hydrogen (classifications E7015 and E7016) and low hydrogen iron powder (classification E7018, E7028 and E7048) electrodes are the most critical types for moisture absorption. These electrodes are manufactured to contain less than 0.6% of moisture in their coverings and are required according to presently acceptable welding standards and procedures for building to be handled with considerable care. In particular they are required to be maintained at an ambient temperature of 30 degrees C plus or minus 10 degrees C and at 50% maximum relative humidity.
On the other hand, coverings for the classification E6010 and E6011 electrodes have different maintenance requirements and are not within the subject matter of this application. These electrodes are required to have moisture levels of from 3 to 7 percent. They are stored at ambient temperature and holding ovens and drying are not recommended prior to their use. These types of electrodes are adversely affected by drying and will cause improper welds if they are subject to drying in an oven or holding at a temperature above ambient.
Porosity is a welding term of art and is a weld defect caused by air bubbles trapped in a weld during the welding process. These bubbles are often caused by using a low hydrogen welding rod (e.g. classification E7018) which has not been kept warm or has cooled down too much prior to being utilized in the welding process. This allows water vapor to enter the well and subsequently during the welding process creates a weal weld of lesser strength than one wherein water vapor has not been allowed to permeate the welding electrode or rod.
It is very important while welding two pieces of metal together with low hydrogen rods to keep the welding electrode or rod within a temperature range between about 30 degrees C and about 150 degrees C. This temperature range has been determined by the industry to be adequate to prevent water vapor from adhering to and permeating the rod and subsequently entering the weld during the welding process. When a weld is not properly executed due to the use of a improperly maintained rod or electrode which has cooled off even partially the coast of repairing such a weld in a building erection environment is often considerable. If the weld is not detected during the initial construction process before the concrete, brick or mortar skin is erected for the particular floor the restructuring process may cost tens of thousands of dollars. If it is caught prior to this time the repair cost may amount to a few hundred or a few thousand dollars.
If a defective weld due to moisture and porosity is detected the entire weld must be removed. The metal parts must then be fitted to each other again and the entire welding process must be executed in its entirely with new electrodes. The bad weld must be ground out. Specifically the bad weld must be removed with a grinder having a hardness greater than that of the two metals joined and of the weld. Alternately, an instrument called an arc gouge may be utilized. Ar arc gouge involves the use of a lead rod with compressed air to cut the bad weld material out with a high temperature torch. Subsequently, a fitter tacks the two ends of the respective metal pieces together and after this procedure is completed the welder must perform the entire welding process again.
For example, welders in the New Jersey area are paid approximately $23.00 per hour and a fitter approximately the same amount. To redo a simple weld not including the time to go up to the site in the case of a multiple story building takes approximately 4 hours for both the fitter and the welder. This means a total cost of 8 hours not including time up the building or time down the building times $23.00 for a cost of approximately $184.00. Even worse when dealing with large diameter pipes repairing and refitting a defective weld might taken any where from a day to a week resulting in a repair cost of approximately $5,000.00. Not only does the cost of replacing a weld have to be considered, if it is a critical weld and a critical aspect of the structure refitting the weld can result in job delays, contract problems and cost overruns involving hundreds of thousands of dollars.
As early as 1886 the concept of utilizing an independent heater or heating element for maintaining a space at a particular temperature was applied in developing a heater for beds, for example in U.S. Pat. No. 354,764 issued to Bell. In 1888 Hiller was issued U.S. Pat. No. 381,549 for a heater for muffs. Hiller's invention is described as a class of minature stoves or warmers employed about the person to emit or throw off heat without burning the parts they may come into contact with. One construction employed a square rectangular box of metal with flat sides and ends perforated with holes. Over the box was placed a layer of fibrous material of cloth. The superimposed layer of cloth was made to hug the outer surface of the metal box as closely as possible so that the heat could pass from the interior of the box directly through the perforations. The heat would otherwise be stored within the box as long as possible with the perforations providing the necessary means for draft of the heated air from the box.
In 1928 France issued Patent No. 638,378 for an insulated elongated receptacle means capable of holding and retaining the temperature of a rod inserted into an inner cavity.
In 1892 Potts was issued U.S. Pat. No. 468,946 for an appliance made of a number of small segments of a material capable of being heated and holding heat and enveloped in a cover used to prevent it from burning the skin.
In 1897 Belgium patent No. 21,548 was issued to Eloy for an apparatus employing as a source of heat a highly needed metal bar placed in a sheet having double sides filled with a material adapted to absorb and slowly emit heat given off by the bar to heat carriages and railway cars.
In 1976 U.S. Pat. No. 3,976,049 was issued to Yamashita et al. for a chemical warmer comprising a pouch adapted to accommodate an exothermic composition whereby heat is produced from the oxidation of iron powder for the purpose of creating and keeping an item warm at a particular temperature. Yamashita demonstrates a heat generating capacity of 49 to 56 degrees C over an ambient of 13 to 17 degrees C for a period of up to 15 hours. The device patented by Yamishita is manufactured by Mycoal Warmers Company, Ltd. of Japan under the trade name GRABBER as a hand a pocket warmer. The GRABBER provides a temperature in a pocket or glove of between 57 degrees C to 69 degrees C for approximately 7 hours or more.